The present invention relates to improvements to the automatic bar feeders for multi-spindle machine tools, and more particularly it relates to a guide device for rotatably supporting bars or elongated material to be fed to a spindle of such machines. The invention also concerns an automatic bar feeder of the rotatable drum type, normally used for selectively feeding bars to be machined by a multi-spindle machine tool.
Guide devices for bar feeders of the aforementioned kind, are described for example in the patents U.S. Pat. No. 4,604,924 and U.S. Pat. No. 4,700,593 or U.S. Pat. No. 4,292,864.
These guide devices generally comprise a first set of fixed jaws and a second set of movable jaws, co-operating to receive and rotatably support a bar to be fed to a spindle of a machine tool; the movable set of jaws of each guide are rotatably mounted to rotate between a closed condition and an open condition of the guide, during each working cycle of the machine tool. A bar-pushing member travels inside the guide jaws to move the bar forwards in correlation with the working cycle of the machine tool.
These guide devices have been previously proposed in substitution of the traditional tubular guides, in particular owing to the possibility of side loading the bars, as shown for example in FIG. 3 of the patent U.S. Pat. No. 4,292,864. However, these known guide devices in practice are subject to several problems resulting from the intrinsic difficulty of using them for supporting and guiding both bars of small diameter and bars of large diameter or having different cross-sectioral dimensions; the specific structure of the guides itself, owing to the presence of a considerable number of hinges and connecting rods, does not allow easy assembly and rapid removal of the guides, sometime necessary for replacing the jaws and worn parts.
In fact, in the currently known guide devices, both the fixed jaws and the movable ones of each guide are fixedly connected to cylindrical rods which are fixed or hinged to support members arranged circumferentially and axially spaced on a rotatable central drum, to provide each guide device with the necessary structural continuity. The presence of several connecting rods and the considerable number of hinges results in considerable assembly and maintenance difficulties which, in the case of feeders of rotating-drum type, associated with machine tools operating at high-speed, or supplied with bars of large diameter, give rise to high noise levels as a result of the vibrations produced by the rapidly rotating bars. Finally, in bar feeders of the known type, the arrangement, in the space between adjacent guides, of the hinges and control levers which negatively effect the opening and closing movements of the guide, resulting in an extremely complicated structure and larger dimensions which considerably reduce the opening angle of the movable jaws of the guides, thus making it difficult, if not sometimes impossible, to load bars having large thickness.